The present invention relates to an underwater detecting apparatus for performing measurement of water depths, detection of a school of fish, or the like by using ultrasonic waves, and a depth measuring apparatus having the same function. Besides, the present invention relates to a display apparatus which is installed in a ship or the like and displays an alarm on a screen in an emergency, and which is provided with a function of displaying guidance as to a key, and a depth measuring apparatus having the same function.
A depth measuring apparatus in which an ultrasonic signal is emitted into the water from an echo sounder transducer provided on a ship's hull and the water depths are measured on the basis of received echo signals, has been conventionally used. In such a conventional depth measuring apparatus, measured data are recorded on a recording sheet and are outputted.
However, in the conventional depth measuring apparatus, paper as a recording medium is used, and this is a consumption article so that this is costly, and this is also inconvenient in handling such as exchange of recording sheets or preservation thereof. Besides, in the depth measuring apparatus of such a recording sheet system, a mechanism for making a record on the recording sheet, and this mechanism includes movable portions such as a gear and belt, so that there is also a problem that the apparatus is inferior in reliability.
Then, instead of the above recording sheet system, it is conceivable to make a system in which measurement data are displayed on a display instrument such as a liquid crystal display. According to this, the recording sheet becomes unnecessary, and data can be electrically stored, and further, any movable mechanism is not necessary, so that the reliability is improved, and the defects of the conventional apparatus can be overcome.
However, since a display instrument mounted on a ship is generally small and the space of a display screen is also limited, when a depth measurement result is displayed on the screen, it is demanded that the largest possible amount of information is displayed efficiently and to be easy to see.
Besides, a ship is equipped with various measuring apparatuses such as a radar apparatus, a fish finder, a tidal current meter, a water temperature meter, and a depth measuring apparatus, and information measured by these apparatuses is displayed as an image on a screen of a display instrument. Here, for example, when a water depth to the seabed measured by the depth measuring apparatus becomes a definite value or less, since there is a fear that the ship strands, that must be informed by an alarm. Thus, it is designed such that the alarm to indicate water depth abnormality is displayed on the screen of the display instrument of the depth measuring apparatus, and this alarm is also given by sound. The depth measuring apparatus provided with such an alarm display function is disclosed in, for example, Japanese Patent Unexamined Publication No.223583/1993.
At the time of a night cruise or the like of a ship, since the surroundings of the display instrument in a room are dark, when the brilliance of the display instrument is raised, a reflection is formed in a glass window or dazzle is given to a navigator, so that it is not preferable in view of safety of the cruise. Then, at a place where the surroundings are dark, the display instrument is set at low brilliance when in use.
However, in the case where some alarm is raised in a state where the display instrument is set at low brilliance, the contents of the alarm displayed on the screen are difficult to understand, since the display screen is dark. In order to accurately grasp this, the brilliance of the screen should be again set at high brilliance to confirm the alarm. Thus, it takes a time to take measures, and there has been a danger that a serious accident such as stranding is caused by a time delay during this. Besides, in an instrument which gives an alarm by sound as well, in the case where there are noises in the surroundings, it is difficult to recognize the alarm sound, so that the danger is further increased.
Besides, a ship is equipped with various measuring apparatuses such as a radar apparatus, a fish finder, a tidal current meter, a water temperature meter, and a depth measuring apparatus, and information measured by these apparatuses is displayed as an image on a screen of a display apparatus. In the display apparatus, an operation portion in which a plurality of keys are arranged is provided, and these keys are operated so that various settings, instructions and the like are executed.
For example, in a depth measuring apparatus, since the position of the bottom of a ship on which a transducer of an ultrasonic beam is provided is not coincident with the position of the sea surface, a draft value of a difference therebetween is inputted through a key in advance, and a correction of a water depth value is performed by using this draft value when the water depth is calculated. Besides, in order to prevent stranding of a ship, an alarm water depth value is set by a key, and when the water depth to the seabed becomes this or less, an alarm is activated.
By the way, since various keys are provided on the operation portion, it is difficult for a person unskilled in the operation to completely understand and memorize the functions of the respective keys. Thus, in general, this kind of apparatus is provided with a help function for displaying guidance as key functions. That is, when a mode is set to a help mode and a predetermined operation is performed, an explanation of the function, operation procedure, and the like for each key are displayed on the screen, and an operator performs the key operation while referring to this. By using such help function, the load of operation is reduced, and the operator can perform a desired key input without puzzlement.
However, in a conventional apparatus, after the mode is set to the help mode, in order to display the guidance of the key, it has been necessary to search and select an item (function, key name, etc.) related to the key from the menu or contents displayed on the help screen. In this case, when the menu or contents are hierarchically constructed, the screen is changed every time the item is selected, and it is necessary to repeat such an operation that a related item is searched and selected on the switched screen, so that a lot of trouble is required.